J.W. Ponton

Systematic construction of dynamic models for phase equilibrium processes

Abstract A systematic approach to constructing dynamic models involving phase equilibrium is presented. The view appears to be widely held that the dynamic modelling of VLE systems invariably leads to an “index problem”. We show that this in general is not the case if an appropriate model formulation is used. This is provided by our systematic procedure. Index problems do in general occur when a state variable is constrained by an implied control system. Some properties of such systems are discussed and it is shown that it may not in practice be useful to attempt the solution of intractable index problems, as these may differ substantially from the behaviour of an achievable control system.

Alternatives to neural networks for inferential measurement

Abstract Neural networks have attracted much attention as a means of modelling nonlinear phenomena, for example for inferential measurement in process control. A neural network is a nonlinear multivariable function whose main potential advantage: the ability to represent highly nonlinear input—output relationships, is in fact not essential in many potential process engineering applications. This advantage is in any case frequently outweighed by its major disadvantage: the intractability of the parameter estimation procedure resulting from the highly nonlinear form of its parameters. In this work we show how moderately nonlinear functions, with easily estimated parameters may be used in certain inferential measurement applications for which neural networks have been proposed. These functions are as effective in representing input—output relationships and their parameters can be fitted far more rapidly than can the “weights” of a neural network. Furthermore, we show that the performance of both these functions and neural networks, being arbitrary representations having no physical basis, may almost invariably be improved upon by the use of even very simple approximate models based on proper physical understanding.

Degrees of freedom analysis in process control

Abstract In developing the control system for a process it is desirable to know precisely the number of process variables which the system designer is entitled to attempt to regulate, commonly known as the “degrees of freedom” of the process. An extremely simple procedure is described; the maximum degrees of freedom for any process is shown to be the total number of process streams, including streams of heating and cooling media. If inventory in processing units is excluded unless, it affects some more significant variable, such as pressure or composition, then the effective degrees of freedom are generally determined by subtracting one from the total for every additional phase contained in a unit.

Experimental and predictive approach for determining wet air oxidation reaction pathways in synthetic wastewaters

The wet air oxidation of aqueous solutions of aniline over a Ru/CeO 2 catalyst was investigated. Batch oxidation experiments were performed at temperatures between 160 and 230C and an oxygen partial pressure of 2 MPa. Liquid phase reaction intermediates were identified and their concentration-time profiles were followed by means of high-performance liquid chromatography. Gas chromatography was also used to follow the concentration of carbon dioxide formed; therefore the extent of total oxidation that had occurred was measured. Based on the experimentally determined reaction intermediates a reaction mechanism for the oxidation of aniline was proposed. In addition a computational approach based upon thermodynamics was used to determine possible reaction pathways. It appears that the theoretical and experimental approaches are in good agreement and provide complementary information that can be used for refining reaction pathways.

Dynamic process simulation using flowsheet structure

Abstract A technique is described for the dynamic simulation of chemical processes which enables an implicit integration method to be used, efficiently and economically, to solve the ordinary differential equations which arise in such simulations. This technique has been used to convert an existing steady state “flowsheet” simulator into a dynamic process simulator. The technique uses the structure of the process and its equation to avoid the generation and manipulation of the Jacobian matrix normally associated with implicit integration methods. The major advantage of such methods, namely the ability to integrate sets of stiff equations with timesteps greater than the smaller time constants, is retained.

An automated procedure for multicomponent product separation synthesis

To date most separation synthesis work has been directed towards the sharp separation, pure component product problem. However, there exist separation processes, particularly in the petroleum industry, which are concerned with the manufacture of multicomponent products. Many of these are effect products, i.e. products whose specifications are in the form of property such as density or vapour pressure and therefore are satisfied by a region of compositions. Such products present opportunities for the use of non-sharp separations and stream splitting and blending, yet no systematic synthesis method which exploits these has been developed. An automatic procedure for the solution of multicomponent product synthesis problems is presented which does not require an explicit superstructure. Separator functions are not predetermined and systematic stream splitting and blending are included. The synthesis algorithm employs a depth first tree search in order to locate solutions and unit design variable discretisation to reduce the search space. The algorithm generates a set of good, feasible solutions which may be further optimised by continuous means.

The ECOSSE Control HyperCourse

Abstract The ECOSSE Control HyperCourse is a course in process control available on the World Wide Web. It is used by undergraduates as a supplement to lectures, tutorials and experiments. It is also intended as a refresher or extension course for process engineers in industry. In this paper we describe some features of this novel approach to control teaching. In particular we show how the teaching material is presented in a variety of ways from simple lecture notes through to interactive simulations of laboratory control experiments.

épée : a process engineering software environment

Abstract We describe the development to date of epee , an object oriented process engineering software environment, epee provides interfaces to a set of standard, but extensible, process engineering objects such as processes , streams and components . It provides user interfaces, such as graphical editors, to create and manipulate these objects. Most importantly, epee provides standard software interfaces to objects, to enable a wide range of applications: flowsheeting, synthesis and design programs, to communicate with the objects and hence each other and with users.

The use of multivariable rational functions for nonlinear data representation and classification

Abstract Multivariable rational functions provide a richly nonlinear representation which also incorporates strong intervariable nonlinear interactions, within a reasonable number of adjustable parameters. They are thus a convenient means of representing arbitrary relationships, even in circumstances where these are quantized or discontinuous. They are mathematically well-defined, and readily fitted using either special or general least squares techniques. The use of these functions in representing complex data is illustrated in examples which include pattern recognition and physical property prediction.

A two-level approach to chemical plant and process simulation

Abstract It is proposed that most unsteady-state simulation problems in chemical engineering fall into one of two categories: (a) those problems which involve pressure-flow interactions of short time scale, but no significant composition changes; and (b) those dominated by composition changes with long time scales. Different modelling techniques are suggested for these two categories and methods for the first are discussed in detail. A two-level technique for combining both methods is described for the solution of problems where both pressure, flow and composition changes must be considered.